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Moth of the Week
Hornet Moth
Sesia apiformis
The hornet moth is a part of the family Sesiidae or the family of clearwing moths. They get their common name predictably from how they mimic the appearance of the hornet. This type of mimicry is called Batesian mimicry, which is when a harmless species mimics the appearance of a unpalatable or defended species to protect themselves from predators. It was first described in 1759 by Carl Alexander Clerck under the name Sphinx apiformis.
Description This moth uses what called Batesian mimicry to resemble the hornet so predators do not want to eat it for fear of being stung. The adult moths have clear wings with yellow and striped black bodies. The number of stripes varies, females have two stripes while males have three. They are about the size of a hornet with the same jerky flight pattern when disturbed. The only difference is the hornet moth has more yellow and lacks the waist between the abdomen and the thorax.
Wingspan Range: 34 - 50 mm (≈1.34 - 1.97 in)
Females are larger than males
Diet and Habitat The larvae eat several species of poplar trees such as apsen (Populus tremula), black poplar (Populus nigra), and goat willow (Salix caprea). They prefer trees surrounded by heavy vegetation as those kinds show more evidence of infestation from larvae burrowing into trees. Adults do not eat.
This moth ranges over mainland Europe, Great Britain, and parts of the Middle East. It had also been introduced to America and Canada. They prefer open habitats such as parks, hedgerows, golf courses, quarries, fens, pond edges, and pits.
Mating The female moths attract males using special posterior glands to emit pheromones, usually soon after emergence. The male doesn’t seem to have any courtship behaviors as the two sexes are likely to begin mating as soon as they come into contact. Both males and females mate multiple times with different partners before the female beings laying her eggs.
Females prefer to lay eggs on old or isolated trees surrounded by vegetation. Females can lay from hundreds to thousands of eggs and exhibits no parental care. When comparing the number of eggs laid to the number of adults emerging per year, it is clear the large number of eggs laid is to make up for the large mortality rate between the egg and adult stages.
Predators This species of moth is primarily preyed on by magpies and great tits. Interestingly, these birds do not eat hornets despite eating this moth. An explanation for this is since these birds don’t eat hornets, the mimicry is less effective as they have any bad experiences with insects of this coloration. In fact, it can be suggested that the black and yellow coloration has the opposite effect: once the birds realize this moth is harmless and can be easily seen, they begin to actively seek them out.
Fun Fact The hornet moth is seen as a pest in the eastern United Kingdom due to a large dieback of poplar trees from larvae burrowing into them. However this dieback is not inherently caused by the larvae but instead from drought and human influences, which the larvae increase the effect of.
(Source: Wikipedia, Butterfly Conservation)